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Pretty diffraction patterns

  1. Dec 17, 2008 #1
    Hi
    I was wondering whether anyone could suggest ways of making nice diffraction patterns using a red laser. I work at a charitable school in Kazakhstan so am limited in terms of materials. Any suggestions would be appreciated. Thanks
     
  2. jcsd
  3. Dec 18, 2008 #2
    What kind of diffraction patterns do you want to look at?

    Do you have an old CD or DVD laying around? Bouncing a laser off of that, it acts as a diffraction grating.

    You can use two razor blades mounted to make a nice single slit. You can even put a thin wire between them on one end, and make the blade edges touch at the other, and have a continuous variable width single slit.

    I've seen double slits made with two razor blades and a thin wire.
     
  4. Dec 18, 2008 #3
    Turn the lights off in the lounge or kitchen etc .. and fire the laser beam at all sorts of stuff ..

    Personally i like aiming at frosted or florescent light bulbs , but you will find all sorts of objects that work well in this regard (especially glancing angles where you aim at the edge of an object .
     
  5. Dec 18, 2008 #4
    Two more ideas. One that was done at my university and the photos featured in the Serway undergrad text...if you have a beam expander, make the beam larger than whatever small coin you have there. We generally use a penny or a dime, which are 9.25mm and 8mm in diameter, and are suspended by the thinnest thread we can find. When projected in a dark room, with a good expanded beam, you can see the shadow of the coin within the beam on a target some distance away. You will also see a bright spot in the CENTER of the target--a bright spot that can only be there because of diffraction. If it isn't clear, try moving the target closer or farther away--I don't recall the exact distance we used, but it was within an indoor laboratory.

    Also, try stretching a hair straight and shining the laser on it. Try different hairs--see if the students can rank the hairs by thickness based on the diffraction pattern.

    Use a piece of foil--even a candy wrapper--and make a tiny pinhole in it. I have made really small ones by placing the foil on a piece of glass, and tapping the pin on the surface of the foil. You'll see a circular aperture diffraction pattern--bright center spot, alternating dark/light rings.
     
  6. Dec 18, 2008 #5
    I found another I remembered--do you have a decent laser printer and transparency sheets that will work in it?

    http://physics.bgsu.edu/~vanhook/gratings/ [Broken]
     
    Last edited by a moderator: May 3, 2017
  7. Dec 18, 2008 #6
    I love this site! Thank you so much for all these great ideas. I will try experimenting. The laser jet prints look amazing but I don't think we have the laser jet :-(

    P.S. if we were investigating hair width based on the diffraction pattern is there an equation we would need?

    Thanks again!
     
  8. Dec 18, 2008 #7
    I would investigate first without an equation if i was you p.t .
    Bring forth equation from observation is a encouraging cycle .

    Another thing to mention is that by reflecting the coherent bean obliquely off an object you can achieve a primary dispersion pattern ..

    The secondary linear filtering of this pattern through a window can reduce the Photon beam considerably .. which can be interesting .

    Also using some small electric fans as oscillating gates the beam can be further reduced in volume ..

    cheers
     
  9. Dec 18, 2008 #8
    You could "calibrate" the hair-measuring laser setup by using wire of known thickness...maybe magnet wire. Measure the characteristics of the diffraction pattern with the various thicknesses of wire, look for a mathematical relationship between the pattern and the wire thickness, then interpolate or extrapolate to the thickness of the hair.
     
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